2. Impression Materials Impression materials are substances that are used to take and record the shape, size, or position of teeth, appliances, and oral anatomy. These materials may be rigid, plastic, or elastic.

3. Types of Impression Materials 1- Rigid Impression Materials: Rigid impression materials are used where no teeth are present, and material flexibility is unnecessary.

4. 2- Plastic Impression Materials Plastic impression materials are used with or without the presence of teeth. This movable material is employed where some material flexibility is needed for the impression. Types of Impression Materials

5. 3- Elastic Impression Materials Elastic impression materials are used where teeth are present and material must be flexible for removal from the oral cavity or teeth. Types of Impression Materials

6. 4- Elastomeric Impression Materials Elastomeric impression materials are used to make impressions of preparations and for demanding or accurate reproductions. These substances are composed of a base and an accelerator, or catalyst (substance that speeds up the chemical reaction) and can be measured, mixed, and placed in a tray or syringe for use in the mouth. Types of Impression Materials

8. Dental Polymer Materials Dental polymers, known as a synthetic resins or acrylics, are the result of a chemical union of monomer and polymer substances. The chemical union of these chains is called polymerization, also known as curing.

9. Among the substances included in the polymerization process are the following: filler: inert substance added to the polymer to alter or modify the polymer properties. Initiator (agent capable of starting polymerization process): may be light, heat, radiation, or chemicals. activator: reacts with initiator to start polymerization. Dental Polymer Materials

10. Inhibitor (substance that prevents polymerization): maintains storage life. Plasticizer (substance that causes a softening effect): changes hard, brittle resin into a flexible, tough material. composite: polymer matrix bonded to glass particles; used for dental restorations. Dental Polymer Materials

11. self-curing resins: autopolymerization materials that perform the uniting process by means of a chemical union; the activator is present in the polymer powder or base and does not have to be added. heat-cured resins: acrylic materials are united but need outside heat to set up; Dental Polymer Materials

12. Precious and Base Metals Many different metals are used in dental procedures. Some are used in their pure state, and others are used in combination with other metals. A combination of two or more metals is called an alloy

13. Metals are classified as precious metals or base metals. Precious or “noble” metals— gold, platinum, palladium, and silver—are used for crowns, bridges, and dental appliances. Precious and Base Metals

14. Base metal alloys contain less than 25% of noble metals and usually consist of chromium, nickel, and cobalt. They are used in partial denture frameworks or as substitutes for gold alloy. Precious and Base Metals

15. Characteristics of Dental Laboratory Materials Bonding: force of the union of one substance with another substance. Creep: tendency of amalgam to deform under constant applied pressure.

16. Cure process: hardening of the material through auto- (chemical) or light-activated response. Ductility: ability of the material to withstand permanent deformation without fracturing under elongation stress. Characteristics of Dental Laboratory Materials

17. Elasticity: ability of a material to return to its original form when stress is removed. Exothermic : chemical release of heat, as in zinc phosphate cement. Trituration: mixing of mercury with other alloy material to form an amalgam. Characteristics of Dental Laboratory Materials

18. Flow: slow bending or movement of material under its own weight. Galvanization: tendency of certain metals to produce an electrical charge when in contact with each other. Toughness: ability of the material to resist fracture. Characteristics of Dental Laboratory Materials

19. hardness: maximum amount of resistance before penetration or scratching can occur. Hydrophilic (ability to attract and hold water): absorption of water. Hydrophobia (fear of water): giving off or shedding of water. Characteristics of Dental Laboratory Materials

20. Initial set: period of time when material assumes shape but remains pliable. Imbibition (absorption of fluid): taking on of water. Malleability: ability to withstand deformation without fracture while undergoing maximum compression stress. Characteristics of Dental Laboratory Materials

21. Setting time: amount of time required for the material to become as hard as it will be. Tensile strength: maximum amount of pulling stress required to rupture the material. Thermal conductivity: capability of the material to transmit heat. Characteristics of Dental Laboratory Materials

22. Working time: period during which a material can be molded, shaped, or manipulated without any adverse effect upon the material. Yield strength: maximum amount of stress a material can withstand without deformation. Characteristics of Dental Laboratory Materials